Cable operated drum brakes

ABSTRACT

A cable operated drum brake has an internal brake operating lever with a quick-attach device for an operating cable. A cable attachment tube projects from a backplate of the brake and the operating cable has an inner cable with a latching formation on the end thereof and a cable outer sleeve. An end portion of the operating cable is slideable towards the backplate within the tube up to a first position at which further movement towards the backplate is stopped by contact between an abutment on the tube and a cooperating abutment on the cable outer sleeve. When the latching formation has moved past the quick-attach device, the cable is then subsequently moveable away from the backplate within the tube to a second position in which the latching formation is fully engaged with the quick-attach device. A fastener maintains the latching formation engaged with the quick-attach device during subsequent operation.

FIELD

This invention relates to cable operated drum brakes and in particularto arrangements and methods for connecting an operating cable to such adrum brake using a “quick-attach” device.

BACKGROUND OF THE INVENTION

When building vehicles on a production assembly line, the rear drumbrake assembly of a motor vehicle braking system may be pre-assembledbefore being attached to the vehicle body and the parking brake cablesmay be subsequently attached to an internal brake operating leverthrough an opening in the drum brake back plate with a “quick-attachdevice on the internal parking brake lever even though direct access tothe braking mechanism is precluded. Examples of such quick-attach”devices are well known and are shown, for example, in GB patent2,328,257 and U.S. Pat. No. 4,753,325 and form no part of the presentinvention. U.S. Pat. No. 5,311,793 also discloses a different type ofdrum brake actuator in which the quick-attach device comprises aresilient spring member located in a passage between a pair ofcooperating actuating levers acting between adjacent ends of a pair ofbrake shoes [or the ends of a single generally U-shaped shoe of the formshown in EP patent 0392829] the spring member deflects a cable nipple toa latching position on one of the levers and subsequently ensures thatthe nipple does not disengage the latching position on this lever.

One problem with such “quick-attach” devices is that there is no way ofverifying that the cable is successfully latched to the lever until thevehicle braking system is assembled and the parking brake is actuated.This is particularly so for electrically operated parking brakes. Afurther problem with electrically operated parking brakes is that thenormal cable travel required for assembly purposes is a significantproportion of the total cable travel available during an operationalstroke of the actuation mechanism.

The present invention provides a cable operated drum brake which enablesthe successful connection of the operating cable to the parking brakelever to be verified, and also reduces assembly travel in the cable.

STATEMENTS OF INVENTION

According to the present invention there is provided a cable operateddrum brake having;

-   -   an internal brake operating lever for connection with a brake        operating cable,    -   a cable attachment tube projecting from a backplate of the        brake,    -   said operating cable having a cable inner with a latching        formation on an end thereof and a cable outer sleeve,    -   a quick-attach device for maintaining the latching formation in        connection with the lever.    -   an end portion of the operating cable being slideable towards        the backplate within the tube up to a first position at which        further movement towards the backplate is stopped by contact        between an abutment on the tube and a cooperating abutment on        the cable outer sleeve, said first position ensuring that the        latching formation has moved passed the quick-attach device,    -   the end portion cable being subsequently moveable away from the        backplate within the tube to a second position in which the        latching formation on the cable inner is fully connected with        the operating lever, and    -   a fastening means to lock the end portion of the cable in said        second position relative to the tube to maintain the latching        formation fully connected with the operating lever during        subsequent operation of the brake.

Such a cable operated drum brake is particularly suited for use aselectrically actuated drum in disc parking brake but can also be used asconventional manually applied parking brake.

A method of attaching an operating cable having a cable inner with alatching formation on an end thereof and a cable outer sleeve, to a drumbrake having a cable attachment tube projecting from a backplate of thebrake, an internal brake operating lever and a quick-attach device formaintaining the latching formation in connection with the lever, themethod comprising:

-   -   sliding an end portion of the operating cable towards the        backplate within the tube up to a first position at which        further movement towards the backplate is stopped by contact        between an abutment on the tube and a co-operating abutment on        the cable outer sleeve, said first position ensuring that the        latching formation has moved passed the quick-attach device,    -   subsequently moving the end portion cable away from the        backplate within the tube to a second position in which the        latching formation on the cable inner is fully connected with        the operating lever, and    -   engaging fastening means to lock the end portion of the cable in        said second position relative to the tube to maintain the        latching formation fully connected with the operating lever        during subsequent operation of the brake.

The quick-attach device may be provided on a parking brake lever pivotedon a brake shoe.

Alternatively the quick-attach device may comprise a resilient springmember located in a passage between a pair of co-operating levers actingbetween the adjacent ends of a pair of brake shoes or the ends of asingle generally U-shaped shoe the spring member being arranged todeflect the latching formation to a latching position on one of thelevers and to subsequently ensure that the latching formation does notdisengage the latching position.

The abutment on the tube may be formed by the end of the tube throughwhich the cable slides.

Alternatively the abutment on the tube may be formed by an internalshoulder formed in a bore of the tube in which the cable slides or on anend of a sleeve in the bore of the tube.

The cable outer sleeve is preferably provided with an end fitting havingan abutment which co-operates with the end of the tube or the internalshoulder or the sleeve.

The fastening means may comprise a clip which is engaged in a groove inthe end fitting when the cable is in the second position, the clip beingheld against the end of the tube to prevent movement away from the firstand second position.

The clip may be held against the end of the tube by a cap which isclipped over the clip and radially projecting flange adjacent the end ofthe tube.

The clip and cap may be formed as a single component both engaging thegroove in the end fitting.

Alternatively the clip may be held against the end of the tube byintegral tangs on the clip which engage a radially projecting flangeadjacent the end of the tube.

In a further alternative the clip may be held against the end of thetube by an internally threaded collar held captive on the end fittingwhich engages an external thread on the end portion of the tube.

In yet a further alternative the fastening means may comprise a wireclip which extends generally perpendicular to the tube and engages agroove in the end fitting and a hole or a slot or slots in the tube.

The attachment tube may be welded to the backplate.

An attachment sleeve may be provided which has a radially extendingflange for engagement with the inside of the backplate and whichprojects into an end portion of the attachment tube adjacent thebackplate and which incorporates snap connectors which snap into afastening formation formed on the inside of the end portion of the tubeto hold the tube against the backplate. This attachment sleeve may beformed from plastics material.

The attachment sleeve may function as the only means of attachment ofthe attachment tube to the backplate or may be used to initially holdthe tube to the backplate prior to welding. This is particularlyadvantageous when the tube is orientated at an acute angle relative tobe backplate when access to the junction of the tube and backplate maybe restricted.

Preferably the attachment sleeve has an internal bore of the samediameter as the internal bore of the tube to avoid forming ledges orother projections on which dirt may lodge or which may damage any cablesealing boot which may be fitted on the inside of the backplate.

Preferably the end of the attachment sleeve on the inside of thebackplate has formations thereon (eg, axially spaced ribs) which assistin the attachment thereto of a cable guidance spring which guides theinner of the cable towards the quick-attach device.

Again preferably the backplate has one or more formations thereon whichsupport the guidance spring so that the cable inner follows a smoothlycuring path on its way to the quick-attach device. Such a constructiongreatly improves the life of the cable which, particularly when used inconjunction with an electrical actuated and electronically controlledparking brake, may be applied more frequently than in a manuallyoperated parking brake.

The attachment tube may include slots or other openings to allow anywater which reaches the inside of the tube to drain out.

The cable is preferably provided with a rubber boot which at one endseals to the end fitting on the outer cable sleeve and at its other endseals onto the cable inner. This boot prevents water and mud etcentering between the inner and outer sleeve of the cable. This boot ishoused within the tube but during installation of the cable and, as thecable is moved to its first position, may partially enter the guidancespring.

The present invention referred to above will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 shows a section through a cable attachment arrangement of a drumbrake in accordance with the present invention;

FIGS. 2 to 6 show modified forms of the cable fastening means for theattachment arrangement of FIG. 1;

FIG. 7 shows an alternative tube attachment arrangement, and

FIG. 8 shows a typical cable guidance spring run from the attachmenttube to the auto-latching device.

With reference to FIG. 1 of the drawings, there is shown part of a cableoperated drum-type parking brake in which a Bowden cable 11 is attachedto an internal brake lever 12 of the brake. The Bowden cable 11 has aninner cable 13 with a nipple 14 firmly attached to one end and which isslideable within an outer sleeve 15. The nipple is attached to the brakelever 12 using a quick-attach device 10 (shown only schematically inFIG. 1) on the brake lever 12.

Any form of quick-attach device 10 may be employed. For example, asshown in FIG. 1, the quick-attach device may comprise a pivoting latchplate 10 a which is biased to its latching position shown in FIG. 1 by aspring 10 b carried on lever 12. Latching plate 10 a is arranged to bedisplaced (to dotted line position 10 a′) against the action of spring10 b by the nipple 14 to allow nipple 14 to pass the latch 10 a (toposition 14′) so that latch 10 a can snap back to its latched positionthus allowing nipple 14 to be drawn back against latch 10 a and henceconnected with lever 12. This type of quick-attach arrangement is shownand described in more detail in, for example GB patent 2,328,257.

Alternatively, for example, a ramp-type quick-attach arrangement asdisclosed in U.S. Pat. No. 4,753,325 may be used.

The cable is attached to a backplate 17 of the brake via a tube 21having a central bore 22 through which the inner cable 13 and nipple 14can pass. The tube 21 has a shoulder 25 adjacent one end with spigotportion which is welded at 23 a to backplate 17 and has a groove 23 btherein for the attachment of a guidance spring 24 which extends fromtube 21 to lever 12.

Tube 21 has a plurality of spaced holes 28 passing through the tubularsidewall which act as drain holes and allow the escape of water, watervapour, mud etc.

The cable 11 has a cylindrical end fitting 31 with a larger diameterinner portion 37 and a smaller diameter outer portion 36 with an annulargroove 38 located axially between the two different diameter portions.The outer end portion 36 of the fitting 31 has a coaxial circular recess32 which accommodates the end portion of the outer sleeve 15 of thecable 11. A coaxial through bore 33 in the fitting provides a passagewayfor the inner cable 13 but does not permit the passage of the nipple 14.

The inner end portion 37 is a slide fit In the bore 22 and has a hollowspigot 34 thereon on which a rubber bellows seal 35 is mounted. The seal35 acts between the spigot 34 and inner cable 13 to prevent the ingressof dirt and water into the cable.

A cable fastening means is provided in the form of a circlip or E-clip39 which engages groove 38 and a plastics retaining cap 40 whichoverlies clip 39 and snaps over a radially extending flange 26 aadjacent end 26 of tube 21 to hold clip 39 against the end 26 of tube 21as will be described below.

End fitting 31 has a radially extending flange 31 a which acts as a stopto contact end 26 of tube 21 and hence limit the insertion of endfitting 31 into tube 21 as described below.

The method of attachment of cable 11 to handbrake lever 12 is asfollows.

Cable 11 is offered up to attachment tube 21 with the inner 13 and itsnipple 14 projecting therefrom. The larger diameter portion 37 of endfitting 31 is inserted into the tube and the cable outer 15 is pusheddown the tube in direction of arrow X into a “first position” in whichthe flange 31 a on the end fitting 31 contacts the end 26 of the tube.

With the cable in this “first position” the nipple 14 has passedcompletely down the guidance spring 24 and has deflected aside thequick-attach latch 10 a′ (see deflected position 10 a′ of the latchshown in dotted detail) to occupy the position shown at 14′ in FIG. 1thus allowing latch 10 a to snap back into its latch position under theaction of spring 10 b.

The cable end fitting 31 is then moved away from the backplate in thedirection of arrow Y until the nipple engages face 10 c of flap 10 a andthe groove 38 is now outside the end 26 of tube 21.

The circlip or E-clip 39 is now inserted in the groove 38 and theplastics retaining cap 40 snapped over clip 39 to hold clip 39 againstthe end 26 of tube 31 thus securing the cable outer 15 in a fixed“second” position relative to the attachment tube 21.

With the cable held in this “second position” the nipple 14 is ensuredto remain correctly latched with latch 10 a during the future operationof the brake.

As will be appreciated, by allowing the cable to be inserted Into theattachment tube to the “first position” and then drawn back to the“second position” as described above the necessary insertion travel ofthe cable to properly engage the quick-attach latch 10 a does notdetract from the working stroke of the cable. This is particularlyimportant when the cable is operated by an electrical actuator whoseworking stroke is relatively limited.

Also, as will be appreciated, the operator has a positive indicationthat the cable has been inserted far enough into the attachment tube 31to definitely engage the quick-attach latch 10 a when the flange 31 acontacts the end 26 of tube 21. Further, when the assembler draws thecable back to the second position he can feel that the nipple 14 hascorrectly engaged the face 10 c of the quick-attach latch 10 a.

FIGS. 2 to 6 show various alternative forms of fastening means forsecuring the cable outer 15 in its second position.

Referring to FIG. 2, this shows an arrangement in which an E-clip 39 andplastics overlaying retaining cap 40 are moulded as one unit whichengages a larger groove 38 in the end fitting 31.

In FIG. 3 the E-clip 39 engages groove 38 and is provided with integralretent on tangs 40 which engage behind flange 26 a.

In FIG. 4 a wire clip 60 extends generally perpendicular to tube 21 andengages slots 61 in tube 21 and a groove 62 in the larger diameterportion 37 of end fitting 31.

FIG. 5 shows a further clip arrangement in which a clip 70 has one limb71 which engages a groove 72 in the larger diameter portion 37 of endfitting 31 and passes through a hole (not visible) in tube 21. The otherlimb 73 of clip 70 extends around the exterior of tube 21, no slot beingnecessary.

FIG. 6 shows a still further alternative in which the tube 21 isexternally threaded at 21 a and these threads are engaged by a collar 41with internal threads 45 which is captive on the cable end fitting 31 bythe larger diameter inner portion 37 of the fitting. After the endfitting 31 has been moved to its second position a generally C-shapedclip or spacer 51 having a key hole shaped opening therein is snappedinto groove 38. This clip 51, which may be formed from glass filledpolymide or other suitable materials such as mild steel, brass etc.,abuts the end 26 of tube 21 and is held in position by the collar 41screwed on to tube 21. In this arrangement the insertion of the endfitting into tube 21 is limited by a stop (not shown) which may beformed by a step in the bore 22 of tube 21 or by a sleeve within bore 22or other suitable means.

FIG. 7 shows an alternative tube arrangement in which tube 21 isfastened to backplate 17 by a separate plastics attachment sleeve 80.Sleeve 80 has a radially projecting flange 81 for contact with a rearface 17 a of backplate 17. Sleeve 80 projects into the end portion oftube 21 and incorporates snap connectors 82 which engage a groove 83formed in the bore 22 of tube 21. The snap connectors 82 are formed onattachment sleeve 80 by slotting the sleeve at 84. These slots may alsoassist in allowing any liquid which may find its way into bore 22 todrain out.

The attachment sleeve 80 may function as the only means of attachment ofthe tube to the backplate or may be used to initially hold the tube tothe backplate prior to welding. This is particularly advantageous whenthe tube is orientated at an acute angle relative to be backplate whenaccess to the junction of the tube and backplate may be restricted.

The attachment sleeve 80 has circumferentially extending ribs 85 formedthereon over which coils of guidance spring 24 are pushed. As can beseen from FIG. 7 the internal bore 86 of sleeve 80 is the same diameteras bore 22 thus preventing the formation of any ledge on which dirt andother detritus may collect and also assisting in preventing any adverseabrasion of sealing boot 35 which slides up and down bore 22 duringattachment of the cable.

Tube 21 is provided with an externally threaded portion 21 a on which anexternal collar held captive on end fitting 31 may be threadedlyengaged. This collar holds the cable in a fixed position relative totube 21 after the cable has been fully engaged with the quick-attachlatch as described above in relation to FIG. 6.

FIGS. 7 and 8 show the formation of backplate 17 at location 17 b into adepression which holds guidance spring 24 in the correct position sothat the centre line of cable inner 13 passes smoothly from the end 23of tube 21 to the quick-attach latch 10 a along the path S-S as shown inFIG. 8. By defining the path of the cable inner in this manner thesmooth operation of the cable over a long period of time is assured.This is particularly important when the hand brake function is operatedelectrically under the control of an electronic device since the handbrake may be applied on many occasions under the control of theelectronic device when it would not be applied by the vehicle driver.For example, the algorithm of the electronic control device may have afunction which automatically applies the hand brake after the vehiclehas been-stationary for a predetermined period of time and/or when thevehicle comes to rest on an incline.

The invention is also applicable to drum brake actuators of the kinddisclosed in U.S. Pat. No. 5,311,793 in which the “quick-attach” devicecomprises a resilient spring member located in a passage between a pairof co-operating actuating levers acting between the adjacent ends of apair of brake shoes [or, the ends of a single generally U-shaped shoe ofthe form shown in EP patent 0392829] the spring member deflects thecable nipple to a latching position on one of the levers andsubsequently ensures that the nipple does not disengage the latchingposition on this lever. When used in connection with this type of brakeactuator the cable attachment tube 21 described above will extendgenerally perpendicular to the back plate of the brake aligned with thecable run.

1. A cable operated drum brake having: an internal brake operating leverfor connection with a brake operating cable, a cable attachment tubeprojecting from a backplate of the brake, said operating cable having aninner cable with a latching formation on an end thereof and a cableouter sleeve, a quick-attach device for maintaining the latchingformation in connection with the lever, an end portion of the operatingcable being slideable towards the backplate within the tube up to afirst position at which further movement towards the backplate isstopped by contact between an abutment on the tube and a co-operatingabutment on the cable outer sleeve, said first position ensuring thatthe latching formation has moved passed the quick-attach device, the endportion cable being subsequently moveable away from the backplate withinthe tube to a second position in which the latching formation on theinner cable is fully connected with the operating lever, and a fasteningmeans to lock the end portion of the cable in said second positionrelative to the tube to maintain the latching formation fully connectedwith the operating lever during subsequent operation of the brake.
 2. Adrum brake according to claim 1 in which the quick-attach device isprovided on a parking brake lever pivoted on a brake shoe.
 3. A drumbrake according to claim 1 in which the quick-attach device comprises aresilient spring member located in a passage between a pair ofcooperating levers acting between the adjacent ends of a pair of brakeshoes or the ends of a single generally U-shaped shoes the spring memberbeing arranged to deflect the latching formation to a latching positionon one of the levers and to subsequently ensure that the latchingformation does not disengage the latching position.
 4. A drum brakeaccording to claim 1 in which the abutment on the tube is formed by theend of the tube through which cable slides.
 5. A drum brake according toclaim 1 in which the abutment on the tube comprises an internal shoulderformed in a bore of the tube in which the cable slides.
 6. A drum brakeaccording to claim 1 in which the abutment on the tube comprises an endof a sleeve in a bore of the tube in which the cable slides.
 7. A drumbrake according to claim 5 in which the cable outer sleeve is providedwith an end fitting having an abutment which cooperates with the end ofthe tube or the internal shoulder or a sleeve in a bore of the tube inwhich the cable slides.
 8. A drum brake according to claim 7 in whichthe fastening means comprises a clip which is engaged in a groove in theend fitting when the cable is in the second position, the clip beingheld against the end of the tube to prevent movement away from the firstand second position.
 9. A drum brake according to claim 8 in which theclip is held against the end of the tube by a cap which is clipped overthe clip and radially projecting flange adjacent the end of the tube.10. A drum brake according to claim 9 in which the clip and cap areformed as a single component both engaging the groove in the endfitting.
 11. A drum brake according to claim 8 in which the clip is heldagainst the end of the tube by integral fangs on the cup which engage aradially projecting flange adjacent the end of the tube.
 12. A drumbrake according to claim 8 in which the clip is held against the end ofthe tube by an internally threaded collar held captive on the endfitting which engages an external thread on the end portion of the tube.13. A drum brake according to claim 7 in which the fastening meanscomprises a wire clip which extends generally perpendicular to the tubeand engages a groove in the end fitting and a hole or a slot or slots inthe tube.
 14. A drum brake according to claim 1 in which the attachmenttube is welded to the backplate.
 15. A drum brake according to claim 1in which an attachment sleeve is provided which has a radially extendingflange for engagement with the inside of the backplate and whichprojects into an end portion of the attachment tube adjacent thebackplate and which incorporates snap connectors which snap into afastening formation formed on the inside of the end portion of the tubeto hold the tube against the backplate.
 16. A drum brake according toclaim 15 in which the attachment sleeve is used to hold the attachmenttube to the backplate prior to welding.
 17. A drum brake according toclaim 15 In which the attachment sleeve has an internal bore of the samediameter as the internal bore of the tube to avoid forming ledges orother projections on which dirt may lodge or which may damage any cablesealing boot which may be fitted on the inside of the backplate.
 18. Adrum brake according to claim 15 in which the end of the attachmentsleeve on the inside of the backplate has formations thereon whichassist in the attachment thereto of a cable guidance spring which guidesthe inner of the cable towards the quick-attach device.
 19. A drum brakeaccording to claim 18 in which the backplate has one or more formationsthereon which support the guidance spring so that the inner cablefollows a smoothly curving path on its way to the quick-attach device.20. A drum brake according to claim 1 in which the attachment tube mayinclude slots or other openings to allow any water which reaches theinside of the tube to drain out.
 21. A drum brake according to claim 7in which the cable is provided with a rubber boot which at one end sealsto the end fitting on the outer cable sleeve and at its other end sealsonto the inner cable.
 22. A method of attaching an operating cablehaving a inner cable with a latching formation on an end thereof and acable outer sleeve, to a drum brake having a cable attachment tubeprojecting from a backplate of the brake, art an internal brakeoperating lever and a quick-attach device for maintaining the latchingformation in connection with the lever, the method comprising: slidingan end portion of the operating cable towards the backplate within thetube up to a first position at which further movement towards thebackplate is stopped by contact between an abutment on the tube and aco-operating abutment on the cable outer sleeve, said first positionensuring that the latching formation has moved passed the quick-attachdevice, subsequently moving the end portion cable away from thebackplate within the tube to a second position in which the latchingformation on the inner cable is fully connected with the operatinglever, and formation fully connected with the operating lever duringsubsequent operation of the brake.